Investigation into the role of autophagy protease ATG4A in normal and impaired erythropoiesis

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PROJECT SUMMARY/ ABSTRACT Autophagy is a self-degradation pathway that has tissue-specific functions in erythropoiesis. During erythroid differentiation, autophagy facilitates the degradation of macromolecules and the programmed clearance of mitochondria. The long-term objective of this proposal is to determine how autophagy contributes to normal and impaired erythropoiesis. Patients with Myelodysplastic syndromes (MDS) often have impaired erythropoiesis and mitochondrial dysfunction. A subset of MDS, MDS with ring sideroblasts (RS), contain the aberrant accumulation of iron-laden mitochondria in erythroblasts suggesting that autophagy may be dysregulated in hematopoietic disorders and impair erythroid differentiation. While essential autophagy genes are known to contribute to autophagy in erythropoiesis, little is known about the tissue-specific regulation of autophagy during human erythroid differentiation. We have identified the selective expression of the autophagy protease ATG4A in the erythroid lineage. We have evaluated the contribution of ATG4A in an ex vivo model of human erythroid differentiation. Early in differentiation, ATG4A promotes the expansion and colony formation of erythroid progenitors. Late in differentiation, ATG4A promotes terminal maturation, enucleation, and mitochondrial clearance. Since ATG4 proteases are regulated by reactive oxygen species, the function of ATG4A in erythropoiesis may be sensitive to oxidative stress. Based on our preliminary results, we hypothesize that ATG4A mediates autophagy during early and late erythropoiesis and is dysregulated by oxidative stress. In aim 1, we will identify the role of ATG4A-dependent autophagy in early erythropoiesis. In aim 2, we will determine the mechanism of ATG4A-dependent mitochondrial clearance. In aim 3, we will examine the regulation of mitochondrial clearance in human models of MDS-RS. The experiments outlined in this proposal will be conducted under the mentorship of Dr. Sergei Doulatov, an expert in the development and use of human iPSC models to study erythroid disorders, and co-mentorship of Dr. Janis Abkowitz, Chair of the Division of Hematology at the University of Washington and international expert in MDS and erythroid biology. This career development award will support my training to become an independent investigator studying the contribution of autophagy to normal and dysfunctional erythropoiesis.